The present invention relates to a method for the removal of waste material in punching units with co-operating rolls, one of which has a number of holes arranged to pick up the waste material punched out. The invention also relates to an apparatus for the realization of the method.
In the punching of a repeated pattern on a material web in general, rotary punching is applied making use of a male roll provided with projecting punches and a female roll provided with corresponding recesses. The material web may consist, e.g., of a laminated packing material which, with the help of a packing machine is to be gradually converted to packing containers of the non-returnable type for juice, milk or other beverages. In cases where it is intended for the beverage to be drunk directly from the packing container with the help of a suction tube, the material web is provided with suction tube holes in a predetermined pattern corresponding to the shape of the individual packing containers. The holes are provided by advancing the material web in the nip between the punching rolls so that suction tube holes are produced according to the desired pattern. Thus, the waste material is produced in the form of small punched-out discs which have to be collected so that they do not land on the ready-punched web or in some other undesirable place. Since the waste material discs are small and light it is very difficult, because of the high punching and feeding rates, to collect and remove them.
Up to now the waste material was usually removed via internal ducts in the female rolls. The recesses or holes in the roll surface were connected to an inner cavity in the roll, this cavity in turn being joined to a vacuum source so that the punching waste is sucked away from the punching region in the nip between the rolls. Owing to problems of seal-forming and noise, the vacuum has to be kept within certain limits. The method, therefore, has a natural limitation which makes it unsuitable for use at high punching speeds, since the rotation of the female roll causes an outwardly directed force which counteracts the vacuum and leads to the waste material sometimes sticking in the holes or even being blown on to the outside of the roll.
It is an object of the present invention to provide a method for overcoming the above problem.
It is a further object of the present invention to provide a reliable and simple method for the effective removal of waste material even when the rotary punching takes place at very high speeds.
These and other objects have been achieved in accordance with the invention with a method for the removal of waste material in a punching unit with co-operating rolls. One roll has a number of holes, each containing a piston arranged to pick up the waste material that has been punched out. The piston is moved during the rotation of the roll between an inner and an outer position so as to retain and then eject the waste material.
In accordance with the invention a strong vacuum is provided during a very short period in the holes which retain the punched out waste material, whereupon they are mechanically pushed out of the holes and sucked away. The event is synchronized with the rotation of the rolls and provides for very safe and rapid handling of the waste material.
It is a further object of the present invention to provide an apparatus for the realization of the method in accordance with the invention. This arrangement is capable of operating at great speed and reliability, and is not subject to the disadvantages of earlier arrangements.
It is a further object of the present invention to provide an apparatus for the removal of waste material in rotary punching. The apparatus has a simple and reliable design capable of being turned out at low cost.
These and other objects have been achieved in accordance with the invention with an apparatus of the type described in the introduction. Each hole comprises a piston which is axially movable in the hole. The piston is in substantially air-tight contact with the wall of the hole, and contacts manoeuvring elements for the displacement of the piston between different axial positions during rotation of the roll.
By placing the pistons directly adjoining the region where the vacuum, a maximum vacuum is achieved which safely retains the punching waste in the die hole. The simple design of the unit and the direct control of the axial movement of the piston by means of a cam track also guarantee an accurate synchronization between the movement of the piston and the rotation of the roll.
A preferred embodiment of the method as well as of the apparatus in accordance with the invention will now be described in more detail with special reference to the enclosed schematic drawings which only show the parts necessary for the understanding of the invention.